Correlation between the Oral and Mental Health of University Students in Serbia—A Cross-Sectional Study

Background: This cross-sectional study aimed to assess the correlation between subjective oral health status and mental health in a group of university students in Serbia. Methods: The study included 948 students, aged between 18 and 27, from the Faculty of Medical Sciences, University of Kragujevac, Serbia, and was conducted in 2020. The World Health Organization’s Oral Health Questionnaire for Adults was utilized to evaluate the respondents’ self-perceived oral health and oral hygiene practices. The existence of depressive symptoms was evaluated using the Beck Depression Inventory-II (BDI-II), and the Zung self-rating anxiety scale (SAS) was used for determining anxiety symptoms. Results: It is observed that 28.9% of respondents exhibit symptoms of depression and 42.3% showed symptoms of anxiety. Results show that students with severe depression and anxiety symptoms very often reported lower self-perceived oral health and oral health problems. Although the nature of this relationship has not been thoroughly evaluated, several studies have shown a mutually dependent connection between oral health and mental health. Conclusions: The results suggest that some aspects of oral health are associated with higher risks of developing symptoms of depression or anxiety, and vice versa.


Introduction
Worldwide in 2019, 280 million individuals, including 23 million children and adolescents lived with depression.Anxiety disorders, as one of the most frequent mental disorders, were present in 301 million individuals, including 58 million children and adolescents [1].
It is generally acknowledged that dental health is important for overall health.Both dentistry and medical students are required to be well aware of oral health issues and to promote oral health in the general public [2].
The World Health Organization (WHO) has recently engaged in extensive epidemiological research with the aim of identifying and validating the connection between mental conditions and physical issues.
Individuals with depression or anxiety problems receive dental care far less frequently and have a roughly 30% higher risk of tooth loss than those with good mental health.Notable risk factors for developing oral disorders include depression and anxiety disorders, particularly for bruxism, which can lead to tooth abrasion and overextension, temporomandibular joint disorders (TMDs), and eventually loosening of teeth [2].
Despite compelling evidence supporting the interdependence between mental illnesses and other health conditions, little is known about how dental health affects these conditions.At least half of dental patients are said to experience anxiety before their appointments, and part of them can even develop anxiety disorders.This relationship is still disregarded even though there is growing evidence that people with mental health issues have poor oral health [3].
Medical school environments are extremely demanding, which can lead to high levels of anxiety, among other health issues, as well as having an impact on a student's academic performance [2].
People who suffer from mental illness are more likely to have oral health issues due to poor nutrition and oral hygiene, excessive consumption of sugary drinks, co-occurring substance abuse (tobacco, alcohol, psychostimulants, etc.), and/or barriers to dental care due to cost or other factors [4].
There is a scarcity of research on the connection between mental health and oral health status among university students in Serbia.This cross-sectional study aimed to analyze the association between subjective oral health status and mental illness in a group of university students in Serbia.

Study Procedure and Participants
Students who were enrolled in the study that was enacted from January to March 2020, attended medical, pharmacy, dentistry, and basic vocational studies at the Faculty of Medical Sciences, University of Kragujevac.Out of 948 participants (age ranging 18-27 years), 48 did not disclose their gender.However, out of those who did, 78% (n = 700) were female students, 22% (n = 200) were male students.Questionnaires were handed out in a paper form after the regular classes/lectures, with prior approval of the board of Faculty of Medical Sciences, University of Kragujevac.Students gave their consent to take part in an anonymous survey.Questions/issues that were not fully answered were excluded from the statistical analysis.

Socio-Demographic Data
Components of questionnaire: basic information (gender, age); anthropometric information (weight, height); information about eating/drinking habits (consumption of meat, bread, vegetables, fruits, etc.; consumption of beverages) and information about satisfaction with physical appearance, duration and types of physical activity.

Symptoms of Depression
The BDI-II scale was used to assess symptoms of depression.This scale consists of 21 questions, where each one is graded between 0 and 3 points.Intention was to record a range of depression symptoms the person has encountered throughout the previous week.The rating scale was as follows: 0-13: no/minimal symptoms; 14-19: mild depressive symptoms; 20-28: moderate depressive symptoms; 29-63: severe depressive symptoms [5,6].

Symptoms of Anxiety
The Zung Self-Rating Anxiety Scale (SAS) is a 20-item self-report assessment tool designed to quantify anxiety levels.In response to the claims, a person should answer how much each one applies to them in the one to two weeks leading up to the test.Each query is graded from 0 to 4 using a Likert-type scale (based on these replies: "a little of the time", "some of the time", "good part of the time", "most of the time").To get around the issue of a set response, certain questions are negatively phrased.A raw score of 36 was the proposed cut-off point in 1980, according to recent studies [7][8][9].

Oral Health
The World Health Organization's Oral Health Questionnaire for Adults was utilized to evaluate the respondents' self-perceived oral health, oral health problems, and oral hygiene practices.It includes 16 questions on oral hygiene practices, oral health status, frequency of dental visits, and subjective perception of oral health [10].
The questionnaires were validated and used in the Serbian language [6,9,10].

Statistical Analysis
Statistical analysis was performed using the Statistical Package for Social Sciences software (SPSS Inc., version 19.0, Chicago, IL, USA).Chi-square test was used to determine the relationship between categorical data.We presented only significant results where p < 0.05.Phi-coefficient and Cramer's V were utilized for examining the association between two categorical variables when there are 2 × 2 and more than 2 × 2 contingency tables, respectively.The relationship between dependent variables and a series of independent variables was examined by univariate logistic regression.The risk was evaluated using the OR (odds ratio) size, with a 95% confidence interval.Spearman's correlation coefficient was used for the correlation of the scales.With a total population of 1566 students when the confidence interval is 95% and the margin error is 5%, the representative sample is calculated to be 309 students.Our study included more students than the calculated representative sample (948 participants).

Results
Reliability and internal consistency of a scale BDI expressed by Cronbach's alpha coefficient was assessed as excellent (α = 0.91).The reliability of the scale for anxiety, estimated on the basis of the value of Cronbach's alpha, was somewhat lower compared to the BDI scale, but still acceptable (0.70).
The distribution of the values of the scales did not follow the normal distribution (Kolmogorov-Smirnov test, p = 0.00 for both scales), so accordingly, Spearman's correlation coefficient was used for the correlation of the scales.A strong positive correlation was found between these two scales (Spearman's rho = 0.709).
It is observed that 28.9% of respondents exhibit symptoms of depression and 42.3% showed symptoms of anxiety, see Tables 1 and 2.  While mild symptoms were present in 14.4%, moderate symptoms in 8.8%, and severe symptoms in 4.7% of respondents, the majority of respondents (72.1%) did not experience any signs of depression.In addition, considerably more female students showed symptoms of severe depression (5%) than male students (3.4%), (Pearson = 11.474,df = 3, p = 0.009).However, older participants with severe depression symptoms were reported in a lower percentage (3.7%),compared to their younger counterparts (5.3%).
The relationship between depressive symptoms and the factors that refer to oral health is shown in Table 1.Everyday issues that were very often consequences of poor oral health were discernible and higher in percentage in those with symptoms of severe depression than in those with mild or no symptoms.Students with severe depression reported very often difficulty biting off (4.5%), difficulty speaking (2.3%), dry mouth (4.5%), ashamed of appearance (6.8%), pressure/discomfort (6.8%), avoiding smiling (7.0%), interrupted sleep (9.1%), difficulty in everyday activities (4.5%), and reduced social interaction (6.8%).However, absence from college was solely significant in male respondents (p = 0.000), with 57.1% of males with severe depression symptoms stating that they were not absent from work/college due to oral problems.Subjectively, reported conditions of teeth and gum are notably different in male students, where 14.3% of male students with symptoms of severe depression reported bad teeth condition in comparison to 0.0% of those with no or mild symptoms.Very bad gum condition is disclosed in 2.9% of female students who displayed symptoms of severe depression, in contrast to 0.0% without the same symptoms.A higher percentage of students who showed symptoms of severe depression (65.1%) used fluorides than students with fewer depression symptoms.
The relationship between the Zung Self-Rating Anxiety Scale (SAS) and the factors regarding oral health are shown in Table 2. Excellent teeth condition was reported in 36.5% of female students with an anxiety score lower than 36, and 28.4% who showed symptoms of anxiety.As for gum condition, the answer, excellent, was given by 50.6% of female students who showed minimal or no anxiety symptoms, and 37% with anxiety symptoms.Statistically significant were the everyday issues concerning oral health, including difficulty biting off (p = 0.009), difficulty chewing food (p = 0.007), difficulty speaking (p = 0.003), dry mouth (p = 0.000), being ashamed of one's appearance (p = 0.000), pressure/discomfort (p = 0.000), avoiding smiling (p = 0.002), interrupted sleep (p = 0.000), difficulty in everyday activities (p = 0.000), and reduced social interaction (p = 0.021).
All values of Cramer's indicator indicate a weak connection between the variables (weak influence according to Cohen's criteria) (Tables 1 and 2).
Regression analysis in the total population did not show a significant association of symptoms of depression and anxiety with oral health in students, except for the variables of difficulty in everyday activities, interrupted sleep, and pressure/discomfort in the multivariate model (Table 3).However, the results of logistic regression by gender, related to oral health, showed that female participants, who very often felt pressure and discomfort (OR = 12.548, p = 0.01), avoided smiling (OR = 12.968, p = 0.006), had difficulties in daily activities (OR = 22.321, p = 0.002), and had less social interaction (OR = 14.133, p = 0.004), had a significantly higher chance of manifesting more serious symptoms of depression compared to those who answered negatively.Female students who very often felt pain and discomfort (OR = 1.596, p = 0.003), used cigarettes (OR = 2.748, p = 0.005), had dry mouth (OR = 6.080, p = 0.002), felt pressure and discomfort (OR = 8.565, p = 0.045), and had sleep interruptions (OR = 15.993,p = 0.001) had a statistically significantly higher chance of exhibiting anxiety symptoms compared to those who answered negatively.Women who sometimes had a problem with biting food (OR = 1.888, p = 0.012), chewing (OR = 12.985, p = 0.000), speaking (OR = 3.716, p = 0.001), and difficulties in daily activities (OR = 2.852, p = 0.001), also had a statistically significant higher chance of exhibiting symptoms of anxiety compared to those who answered negatively.When it comes to male counterparts, those who very often felt embarrassed (OR = 23.120,p = 0.018), avoided smiling (OR = 24.000,p = 0.016), had interrupted sleep (OR = 14.167, p = 0.006), and had fewer social interactions (OR = 12.000, p = 0.043) had a significantly higher chance of exhibiting more serious symptoms of depression compared to male students who answered negatively.Male participants who had the best dental condition (OR = 0.019, p = 0.019) had less chance of more serious symptoms of depression.Men who used cigarettes very often (OR = 1.860, p = 0.05) and had interrupted sleep (OR = 6.729, p = 0.026) were statistically significantly more likely to exhibit symptoms of anxiety compared to those who answered negatively.

Discussion
Correspondences between mental conditions and dental health are uncovered every year; despite this, the connection is still overlooked.
A meta-analysis by Quek et al. [11] revealed that anxiety was more common in female medical students than in male students, but without a statistically significant difference.Our findings indicate a statistically significant difference between males and females, with females having a higher prevalence of anxiety symptoms.
Studies by Pitułaj et al. and Okoro et al. [3,12] exhibited that participants who had shown anxiety or depression symptoms utilized dental services less frequently; however, in our study, there was no significant difference in those with and without anxiety and depression symptoms regarding the time of the last visit to the dentist.
In comparison to a previous study by Stepovic et al. [13], where no statistically significant difference was found when examining the relationship between gender and the BDI scale, our study showed considerably more female students had shown symptoms of severe depression than male students.Moreover, our study showed no significant difference regarding the correlation between symptoms of depression and the frequency of toothbrushing, contrasting with the above-mentioned study [13].However, our study showed that 14.3% of male respondents with symptoms of severe depression reported bad teeth condition in comparison to 0.0% of those with no or mild symptoms, which contradicts the findings of related research carried out on Serbian students, which indicated that a greater proportion of male respondents without depressive symptoms had poor oral health than those with symptoms [13].
Smoking is more common in people with anxiety symptoms according to the previous research, which is in agreement with our research.Analysis of the data showed a significant difference in females (30.2%) and males (42.9%) with symptoms of anxiety who reported themselves as smokers [14].
In contrast to our study, where younger students more often reported severe depression (5.3%) and anxiety (48.8%) symptoms, in China, older medical students had a higher prevalence of the above-mentioned symptoms [15].
Although the nature of this relationship has not been thoroughly evaluated, several studies have shown a mutually dependent connection between oral health and mental health [16] and have tried to elucidate possible reasons for this association.The low priority of oral health, poor recognition of the link between poor oral and mental health by healthcare professionals, and the lack of alternative service models in dental facilities for those with increased anxiety and/or mental health problems have been identified as some of the underlying reasons for this link [17].
However, some studies have shown that depression and anxiety have no effect on dental health.They also showed that men have better oral health, and women have better dental care, and that education is associated with better dental care [18].
Individuals with mental illness are more likely to have suboptimal oral health than those without [19].
Depressive symptoms can negatively affect behavior related to oral hygiene and the treatment of dental diseases.A higher risk of tooth decay and tooth loss may lead to more frequent pain, social isolation and low self-esteem, and reduced quality of life, resulting in poorer mental and overall health [20].
Our study has some limitations.The results of the survey are based on a cross-sectional survey, and all data were self-reported by the participants; hence, there were no objective measures of oral health.We cannot conclude that these results apply to students from other faculties because the student population is from the Faculty of Medical Sciences, and it may be presumed that they already have prior knowledge of the evaluated issue.We intend to acquire similar data in the future to maintain the continuity of research and work to better understand the relationship between mental and oral health over time.Despite these limitations, this study offers a significant contribution to the literature, highlighting the association between oral health status and poor mental health at the population level.Further research is necessary to understand the mechanisms underlying these associations.

Conclusions
A sample of Serbian students was used in our research to examine the relationship between oral health and symptoms of depression and anxiety.
The study showed a significant correlation between common mental health disorders and oral health.
Although the findings are inconclusive and somewhat contradictory as to whether oral health affects mental health or vice versa, we can conclude, based on the previous studies and our results, that there is a mutual and bidirectional correlation between oral and mental health.That is why our study can offer an opportunity to consider whether a more integrated approach to oral health and mental health for students, as well as for the rest of the population, is necessary.Informed Consent Statement: Informed consent was obtained from all subjects involved in the study.

Table 1 .
Symptoms of depression associated with oral health by gender and in total.

Table 2 .
Symptoms of anxiety associated with oral health by gender and in total.

Table 3 .
Regression analysis of depressive and anxiety symptoms associated with oral health in university students.